We have determined that in the second half of pregnancy, the primate myometrium exhibits two distinct types of activity with different pressure waves and electrical characteristics, different patterns related to light-dark cycles and different time relations to surgery and duration of gestation. We hypothesize that changes in estrogen physiology play a causal role in the control of these two types of myometrical activity. We will study and define the role of estrogens in both labor and delivery "contractions" and low amplitude, tonic "contractures". Labor is a multifactorial process with interconnected positive and negative feedback loops. We will focus on the role of estrogens. Good circumstantial evidence points to estrogens as a major factor controlling myometrial activity in primates. Much prostaglandin and oxytocin function is secondary to estrogen physiology. From analogy with sheep and from our's and others' data in monkeys, we hypothesize a major role for estrogens. We have used tethered chronic pregnant monkey preparations at Cornell with delivery of live fetuses up to 58 days after instrumentation. We will use this preparation in our studies to obtain controlled quantitative data for five specific aims, 1) identify the major bioactive estrogen in maternal blood, 2) identify the major bioactive estrogen in fetal blood, 3) study myometrial responses to endogenously generated estrogens, 4) studymyometrial responses to decreased estrogen production, 5) study changes in oxytocin sensitivity. Data will be stored on microprocessor based acquisition systems and computer analysed using both in-house designed and standard Fourrier-transform methods. Most studies on control of parturition and myometrial function have been done in sheep. The many differences in fetal and maternal endocrinology between primates and sheep dictate that a clear understanding of control of myometrial activity in humans awaits controlled experimental data in non-human primates. This information will aid the search for efficacious agents to control premature labor.